This shared instrumentation grant application requests a multiparameter, bench-top flow cytometer, the FACScan System. The FACScan includes: (1) an air-cooled 15 milliwatt Argonion laser; (2) emission optics for three-color fluorescence detection and two-angle light scatter detection; (3) three high-performance photomultiplier tubes; (4) an advanced signal processing system; and (5) a data management system with required research applications software. This system will provide six groups of investigators in the disciplines of cell and molecular biology with state-of-the-art flow cytometry essential for their investigations. It will be an a crucial resource for PHS-supported research on the Medical School campus of the University of California at San Diego.